X-ray spectrometer



. July 5, 1949. I H. FIRIEDMAN 2,474,835

X-RAY SPECTROMETER Filed July 14, 1945 HERBERT FRIEDMAN Patented July 5, 1949 OF F 1 CE 3 Claims.

1 My invention. relates to .a method and apparatus for [taking X-ray diffraction patterns and .particularly it relates to an apparatus -.adap.ted..to the. production of 'X-ray diffraction patternsof .much improved intensity-and their rapid .detec- 'tion and measurement.

Insofarlasthis application disclosessubject .matter common to my prior-filed.app1ications, Serial "Numbers 452,599 and 553,262, filed July "28,1942and September 8,1944, respectively, now .Patents 2,386,785 and 2,428,796 respectively, it maybe considered a continuation-impart thereof.

The general adoption of X-ray diffraction technique in the study andanalysis of chemical compositionshas been hindered by the'fact that available methods for measuringthe relative intensities of patterns and lines in the patterns .have been quite slow. For example, the photographingof an X-ray diffraction pattern, requiresan exposure of many hours in order to bring out.

some of the Weaker lines in the pattern, being studied. In my prior filed application, Serial "No. 452,599, I have disclosed arapid scanning method'for measuring the intensity of an X-ray *diffraction. pattern in. which the radiation sensi- "tive element is a GeigerrMuller counterhavinga very 'high quantum efficiency- Byusingsuchua count-er as a detectorit is possible to scan an .X- ray diffraction pattern of relatively low intensity in a short period of time.

The problemof studying. materials by measuring the intensities of their Xray..diffraction patterns has many aspects, anmimportant one .of .IWhi'Ch. is .the, productionof a pattern of conveni- Lently measurable intensity. Accordingly,lit is an object of this invention toprovide. a methodtand apparatus for producing X-ray diffraction patterns of high intensity withoutthe use of voltages on .thaX-ray tube which are higher than those commonly used.

In X-ray spectrometric work, frequently a large portion of the intensity of the radiation is lost by -absorption of the radiation in air. Hence, it is another object of my invention'to provide an X- ray spectrometerin which the distances between the source of the X-rays, the specimen being .examined, and the detector are reduced to a .minimum, thereby assisting in the production f patterns of increased intensity.

It is the. primary object of my inventionlito provide an X ray spectrometer in which the anode of the X-raytube itself 'canbe used as the first dine-source of X-rays for 1 irradiating the speci- :.men "to vbeuexamined, instead of a slit "assembly ,partsyvfhichare :adaptedto effectsuch steps, all ,as exemplifiedin the following detailed disclosure, and the scope of.the.invention will be indicated in the claims.

are 1 defined by the support has as a center of rotation for detector .Hithe "samecenter of rotation asdoes the ,specimenllli, "nam'el y, "point I1.

amended 'April30,'1928; 370 0. G.757)

,collimation of beam 0f.X-rays.

Other objects andadvantages of my invention Willin part beobvious and in partappear hereinafter.

. My invention accordingly comprises the method of producing ,X-ray-.-diffraction patterns of improvedintensityand includes the several steps and the relationof one or more of such steps ...to each of..the.others, .and theimproVedrX-ray spectrometer adapted to produce intense diffrac- .'tion ,patternsiaccording .to my method which .apparatus embodies the features of construction,

combinations. of elements and arrangement of ;In thedrawing I haveshown, diagrammatically, a plan ,view of the table-of myimproved 'X-ray spectrometer, in order vto show .the inter- ;relationship of the parts.

"Referring to-the drawing, It! represents the .itable top of an X-ray spectrometer, Ii an X-ray tube, t2 the tube anode and 13 a tube window.

(Close to the window there-is mounted a variable slit M which is used to regulate the .divergence of the X-ray beam H3 in order to provide for the irradiation ,of thedesired substantial portion of specimen I6 as indicated, which specimen is mounted in a holder 16a having, a center of rota- '-ti,cn identified as l'l in the drawing. In convention-al apparatus a second slit (or aperture) would be'necessaryibetweenthe vanode and the .divergence-regulating slit to form a line (or point) source of radiation. The diffracted beam, l8, of

*X-rays is intercepted and its intensity measured *"byrbletector [9, Which is mounted in aman-ner such' that it canbe swept through a ninety degree Thesupport .20

"The support 20, specimen I6 and detector .19 are mounted on baseZlwhich is mounted .onthe spectrometer table to have a center of rotation passing through, the

specimen l6 sights the tube anode through the tube window is regulated and controlled by set screws 23 and 24, which can be calibrated to give an actual measure of the angle of sight" as indicated by markings 25.

In the construction of X-ray tubes it is wellknown practice to attempt to focus the high speed electron stream originating at the tube filament as a line on the anode surface. The result is accomplished with greater or lesser degrees of success in different X-ray tubes, but the activated area is always large enough to necessitate the use of a slit assembly in order to achieve a line-source of radiation in conventional spectrometers. The area of the anode surface activated by the bombarding electrons is a source of X-rays every point of which radiates in all directions from the face of the anode.

Conventional X-ray diffraction apparatus have a first slit forming a line source of radiation approximately at the point at which slit I4 has been shown in the drawing and a second slit, to control the beam divergence farther along the beam axis. In the present invention by sighting the X-ray tube anode at a low angle I have been able to use radiation from an appreciable area of the anode as substantially a line, or pointsource of diverging rays in one plane as indicated in the drawing where such one plane is the plane of the paper. I thus eliminate the need for the first slit thereby exposing the specimen to a much more intense irradiation and producing a more intense difl raction pattern.

By establishing several centers or axes of rotation of the specimen and support (several positions of point H) in an X-ray spectrometer substantially as described, I have been able to construct a simple, modified X-ray spectrometer capable of giving X-ray diffraction patterns with intensities increased by a factor of ten or more without the application of additional voltage to the X-ray tube. Provision of base 2!, with an axis of rotation passing through the face of the anode of the X-ray tube defining the center of rotation of the base 2| permits pivoting of the specimen and detector about the axis 22 as a unit. In the drawing, as it is shown, the base carrying the specimen holder and the detector support has been set to an angle such that the X-ray beam is being sighted by the specimen at an angle of about 5 for convenience in representation. Actually the angle of sight can be substantially smaller and, in fact, it is preferable to have it as close to zero as possible. In practice I have found that angles of sight of about 2 to 3 represent good working angles.

The advantages of constructing an X-ray spectrometer to provide for a variable angular relationship among the tube anode, the specimen holder and the diffracted beam detector accrue largely as resulting in patterns of increased intensity. The employment of the tube anode as a first slit source (with respect to the specimen sighting said anode at a low angle) by eliminating one of the slits commonly used in X-ray spectrometers, permits use of the anode of the tube itself as a primary source with consequent strong irradiation. Likewise the sighting of the X-ray tube anode at a small angle permits a more intense irradiation of the specimen. Both of these features make a substantial contribution to increasing the intensity of the pattern with the net result that pattern intensities increased by a facor of at least ten are readily obtained. By sighting the tube anode at angles of 2 to 3 in an apparatus constructed according to the dey scription, I have readily been able to obtain diffraction patterns having intensities increased by a factor of ten and more.

Since different embodiments of the invention could be made without departing from the scope of this invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

Having described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. An X-ray spectrometer comprising, a source of X-rays consisting of an X-ray tube, a specimen holder and a detector, said specimen holder being disposed on a pivot member, the pivot axis of which lies in, and passes through the center of, the face-plane of the anode of said X-ray tube, and said detector being disposed on a support which is rigidly mounted on said pivot member.

2. In an X-ray spectrometer having an X-ray tube equipped with a plane-face anode, said plane-face being substantially perpendicular to the longitudinal axis of said anode and a specimen holder, means for converting the anode of said tube from an area-source into effectively a line-source, comprising, a support for said specimen holder pivotally disposed for movement about an axis lying in, and passing through the center of, the face-plane of the anode of said tube, and means for regulating and indicating the pivotal position of said support and thereby the angle subtended by said support and said anode face.

3. In X-ray spectrometer apparatus, the combination of, an X-ray tube having a plane-face anode substantially perpendicular to the direction of exciting radiation from the cathode of said tube, a specimen holder rotatable through mounted through its axis of rotation on a pivot member, said member having for its pivot axis an element lying in, and passing through the center of the face-plane of said anode, a variablewidth slit assembly mounted on said pivot member, a detector support rigidly mounted on said pivot member and moveable therewith, and a detector disposed on said support and moveable with respect thereto through an arc of 90, said are being that swept out by the major axis of said specimen holder during its rotation, with means for regulating and indicating the pivotal position of said pivot member.

HERBERT FRIEDMAN.

REFERENCES CITED The following referenlces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,589,833 Behnken et al June 22, 1926 2,025,488 Yap Dec. 24, 1935 2,145,686 Dessauer Jan. 31, 1939 2,383,764 Bond Aug. 28, 1945 OTHER REFERENCES The Construction and Use of X-ray Powder Cameras, by A. J. Bradley et al., Journal Scientific Instruments, vol. 18, 1941, p. 218. 

